Purification of alpha,alpha-disubstituted-beta-propiolactones

ABSTRACT

WHEREIN R AND R1 ARE SELECTED FROM THE GROUP CONSISTING OF STRAIGHT- OR BRANCHED-CHAIN ALKYL GROUPS OF FROM 1 TO 10 CARBON ATOMS, SUBSTITUTED OF UNSUBSTITUTED CYCLIC HYDROCARBON GROUPS OF FROM 6 TO 10 CARBON ATOMS, OR WHEREIN R AND R1 JOIN TO FORM A RING OF FROM 6 TO 10 CARBON ATOMS, IS EFFECTIVELY OBTAINED FROM IMPURE MONOMER CONTAINING RESIDUAL MANUFACTURING IMPURITIES BY TREATING THE IMPURE LACTONE MONOMER WITH AN ALUMINUM ALKYL OF THE FORMULA ALR23 WHEREIN R2 IS A LOWER ALKYL GROUP OF FROM 1 TO 8 CARBON ATOMS, AND SUBSEQUENTLY DISTILLING THE PURIFIED MONOMER FROM THE RESULTANT SOLUTION AT REDUCED PRESSURE. THE PROCEDURE YIELDS A VERY PURE POLYMERIZATION GRADE A,A-DISUBSTITUTED-B-PROPIOLACTONE MONOMER WHICH HAS A LOW POLYMERIZATION INDEX AND FROM WHICH A POLYMER HAVING A HIGH INHERENT VISCOSITY CAN BE FORMED.   3-R,3-R1-OXETAN-2-ONE   POLYMERIZATION GRADE A,A-DISUBSTITUTED-B-PROPIOLACTONE MONOMER HAVING THE GENERAL FORMULA

3,825,573 PURIFICATION OF a,a-DISUBSTITUTED- p-PROPIOLACTONES William A.Ames, Longview, and James J. Ward, Henderson, Tex., assignors to EastmanKodak Company, Rochester, N.Y. No Drawing. Filed Dec. 16, 1971, Ser. No.208,906 Int. Cl. 0071! 3/00 U.S. Cl. 260-3433 10 Claims ABSTRACT OF THEDISCLOSURE Polymerization grade a,u-disubstituted-fl-propiolactonemonomer having the general formula RI t-i= H2C O wherein R and R areselected from the group consisting of straightor branched-chain alkylgroups of from 1 to carbon atoms, substituted of unsubstituted cyclichydrocarbon groups of from 6 to 10 carbon atoms, or wherein R and R jointo form a ring of from 6 to 10 carbon atoms, is effectively obtainedfrom impure monomer containing residual manufacturing impurities bytreating the impure lactone monomer with an aluminum alkyl of theformula AlR wherein R is a lower alkyl group of from 1 to 8 carbonatoms, and subsequently distilling the purified monomer from theresultant solution at reduced pres sure. The procedure yields a verypure polymerization grade a,a-disubstituted-fl-propiolactone monomerwhich has a low polymerization index and from which a polymer having ahigh inherent viscosity can be formed.

This invention relates to the purification of fl-lactones. Moreparticularly, this invention relates to the purifica- United StatesPatent 0 tion of B-lactones such as, for example,06,0t-dlSl1bStltLllI6dfi-propiolactones by treating the impure materialwith an effective amount of an aluminum alkyl.

'It is well known that B-lactones are important as intermediates for theproduction of synthetic chemicals, polymer products, pharmaceuticals,and the like. The a,a-disubstituted-fi-propiolactones are of particularinterest in the high polymer industry since they can be used as startingmaterials for the production of synthetic resins and fibers which havemany novel and desirable properties. However, for the lactones to beuseful in the preparation of commercial polymers, they must be of veryhigh purity and quality. Because of their extremely high reactivity dueto the strained four-membered ring, thea,a-disubstituted-B-propiolactones cannot be purified by typicalprocedures used for other monomers. For example, unlike the alkylvinylethers, the a,a-disubstituted-B-propiolactones cannot be purified byrefluxing over alkali metal be cause they will polymerize under theseconditions. Other compounds frequently used for monomer purificationeither initiate polymerization of the lactone or are too inefficient.

Various procedures have been disclosed for purifyinga,a-disubstituted-p-propiolactones. However, they suifer from thedefects of either being quite complicated, laborious, or inefiicient.For example, British Patent 1,122,939, issued to Shell Research,describes a method of purifying pivalolactone by extraction with 2%aqueous Na CO followed by two extractions with H 0 and tripledistillation of the organic phase in the presence of picric acid.

Thus, in view of the aforementioned deficiencies of known methods ofpurification of mgct-dlSIlbStltlltGd-fipropiolactone, a need exists fora simple and effective method of Obtaining polymerization gradeoc,a-diSLIbstiuted-fl-propiolactone.

3,825,573 Patented July 23, 1974 Therefore, it is an object of thisinvention to provide a process for obtaining polymerization grade(B-lactones.

Another object of this invention is to provide a process for obtainingpolymerization grade u,u-disubstituted-B- propiolactones which is simpleand produces a high yield of polymerization grade material.

These and other objects and advantages of this invention will becomeapparent from the following description and appended claims.

In accordance with this invention it has been found that B-lactones, andespecially a,u-disubstituted-B-propiolactones having the general formulaH2(|3CI) wherein R and R are selected from the group consisting ofstraightor branched-chain alkyl groups of from 1 to 10 carbon atoms(i.e., methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, etc.),substituted or unsubstituted cyclic hydrocarbon groups of from 6 to 10carbon atoms (i.e., cyclohexyl, benzyl, phenyl, naphthyl, etc.), orwherein R and R join to form a ring of from 6 to 10 carbon atoms (i.e.,radicals having the formula -CH -(CH ),,-CH

where n is a positive integer of from 3-7, or

CH=CH(CH CH or the like), can be effectively purified to yieldpolymerization grade monomer by treating the impurea,a-disubstituted-B-propiolactone containing residual manufacturingimpurities with an aluminum alkyl having the formula AlR wherein R is astraightor branched-chain alkyl group of 1 to 8 carbon atoms, anddistilling the resultant solution at a reduced pressure. In a preferredembodiment R and R represent straightor branched-chain alkyl groups offrom 1 to 4 carbon atoms. This procedure will yield a very purepolymerization grade D m-disubstituted-B-propiolactone monomer whichpossesses a low polymerization index and from which a polymer having ahigh inherent viscosity can be formed. When used in this specification,polymerization index is considered to be simply a measure of the purityand polymerizability of the monomer. Typically, for pivalolactone, it isdefined as the time (in seconds) required for ten grams of pivalolactonecontaining 0.50 ml. of 0.100N tetrabutylammonium iodide in acetone tobegin polymerizing when placed on a steam cone in an aluminum moisturedish. As will be appreciated, high molecular weight polymer can be madeonly from very pure monomer, hence, monomer with a low polymerizationindex is very desirable. Thus, monomer suitable for polymerizationshould exhibit a very low polymerization index, preferably less than 15seconds, since, generally, the lower the value of the polymerizationindex the greater the monomer purity.

Suitable a,u-disubstituted-fi-propiolactones that can be purified inaccordance with this invention include ct,ot-dimethyl-fl-propiolactone(pivalolactone); a,a-diethyl-[3-propiolactone;a,a-dipropyl-B-propiolactone; a,a-diisopropyl- ,B-propiolactone;a,-dibutyl B propiolactone; 2-ethyl-2- methylhydracrylic acidfi-lactone; 2-(2,2-dimethyloctyl)- 2-methylhydracrylic acid fl-lactone;2-(2-ethylhexyl)-2- ethylhydracrylic acid 8-lactone;2-cyclohexyl-2-propylhydracrylic acid B-lactone;2-phenyl-2-methylhydracrylic acid ;8-lactone;2-benzyl-2-methylhydracrylic acid B-lactone;2,2-pentamethylene-B-propiolactone, and the like. These may be preparedby the general method described in Kung, US. Pat. 2,356,459, dated Aug.22, 1944, wherein a dialkyl ketene is reacted with formaldehyde.

All of the various aluminum trialkyls, whether branched or linear in thealkyl portion of the molecule, are useful.

The lower aluminum trialkyls up to aluminum tripentyl, are preferred.Suitable aluminum trialkyls are aluminum trimethyl, aluminum triethyl,aluminum tri-n-propyl, aluminum tri-n-butyl, aluminum triisobutyl,aluminum tri-nhexyl, aluminum triisohexyl, aluminum tri-n-octyl.

The quantity of aluminum alkyl required depends entirely on the type andpurity of the monomer and the particular aluminum alkyl selected. In anyevent, enough should be used to remove any trace of H 0, alcohol, acid,or carbonyl containing compounds. A preferred amount, for pivalolactone,will be sufficient aluminum trialkyl to lower the polymerization indexof the monomer to less than seconds. Suitable amounts can be calculatedby determining a polymerization index on the impure monomer, then addingabout 1.00 milliliters of 15% aluminum trialkyl in hydrocarbon solvent.per 100 grams of monomer for each 12 to 15 seconds of polymerizationindex. Excessive amounts of the aluminum trialkyls should not be used asthey may initiate polymerization of the monomer. For example, if two tofive times or more of the amount of aluminum trialkyl as specified aboveis added, polymerization of the monomer will generally occur.

In practice, a Weighed amount of the impure lactone is treated with apredetermined quantity of the aluminum trialkyl and the purified monomeris subsequently separated from the resultant mixture. A preferred methodis by vacuum distillation. In the context of thi invention, the impurelactones will normally analyze approximately 99% pure by gaschromatography and have a polymerization index of from about 45 secondsto 120 seconds or greater. The treatment of the impure lactone monomerwith the aluminum trialkyl is carried out at essentially roomtemperature and under an inert atmosphere such as nitrogen. Any gas maybe used as long as it i inert to the reactants. Oxygen must normally beexcluded as it will react with the aluminum trialkyls.

Temperature is relatively unimportant. It has been found that thesolution of impure monomer and aluminum alkyl can be heated totemperatures of 130 C. or more without producing polymerization of themonomer.

This invention will be further illustrated by the following examples ofpreferred embodiments. It will be understood that these examples areincluded merely for purposes of illustration and are not intended tolimit the scope of the invention.

Inherent viscosity, when referred to in these examples, is measured atC. in 60/40 phenol/tetrachloroethane at 0.5 grams per 100 cc.concentration.

EXAMPLE 1 Pivalolactone is synthesized by any of the known procedures toyield a monomer having a polymerization index of 85 seconds. One hundredgrams of the lactone monomer is charged to a clean, dry, 500-ml. flaskfitted with a stirrer, reflux condenser, thermowell, and hypodermicsyringe injection port. The flask is purged thoroughly with N A positiveN pressure is maintained in the 'vessel until the distillation step isbegun. Five ml. of 15 percent aluminum triethyl in mineral spirits iinjected into the lactone with stirring. The stirrer and syringeinjection port are removed after about five minutes. One drop of UnionCarbide SAG-5310 silicone antifoam and several boiling chips are added.The vessel is set up for flash distillation at reduced pressure. Themonomer distills at 38-39" C. at 6 mm. Only a small amount of residueremains in the flask. Yield of recovered monomer is in excess of 90percent. The polymerization index of the purified monomer is 15 seconds.The inherent viscosity of the polymer obtained from the purified monomerin determining the polymerization index is 1.3 wherea thestarting'material yielded polymer with an inherent viscosity of only0.23 at the same monomer-to-initiator mole ratio.

4 EXAMPLE 2 Twelve hundred grams of pivalolactone having apolymerization index of 60 seconds is charged to a clean, drythree-liter flask fitted with a stirrer, condenser, and thermowell. Theflask is purged thoroughly with N and a positive pressure maintained onits contents until the distillation phase is begun.

Thirty-six ml. of 25 percent aluminum triisobutyl in heptane is added tothe flask with stirring. The stirrer is removed after a few minutes.Twelve drops of Union Carbide SAG5310 antifoam is added, and the systemis set up for flash distillation at reduced pressure. The monomerdistills at 3839 C. at 6 mm. pressure. The base temperature is 40 C. Theyield of monomer recovered is 97-98 percent. The polymerization index ofthe aluminum triisobutyl treated pivalolactone is 8 seconds.

EXAMPLE 3 Impure pivalolactone monomer is treated with various amountsof aluminum triethyl by the same procedure given in Example 2. Theresults are shown in Table 1.

TABLE 1.-PURIFICATION OF PIVALOLACTONE WITH ALUMINUM TRIETHYLPolymeriza- Initial tion index Weight of impure Milliliters ofpolymerizaafter puripivalolactone aluminum tion index, fication,Inherent monomer grams triethyl 1 seconds seconds viscosity 1 15%Aluminum triethyl in mineral spirits.

These results illustrate the relationship between polymerization indexand inherent viscosity and the effect of increasing amounts of thealuminum trialkyl. As is readily seen, using the same monomer toinitiator mole ratio, an impure pivalolactone monomer withpolymerization index of 65 seconds yields a polymer with an inherentviscosity of only 0.19, whereas a purified monomer with a polymerizationindex of 5.5 seconds yields a polymer with an inherent viscosity of1.14. The polymer prepared from the 5.5 second polymerization indexmaterial has a molecular weight sufliciently high that it is useful inmanufacturing fibers, films and molded articles. The polymer obtainedfrom the untreated material using the same monomer to initiator moleratio and having an inherent viscosity of 0.19 is essentially worthlessbecause the molecular weight is too low and it is brittle.

The novelty and utility of this invention can be further appreciatedwhen compared with several alternate procedures which were examined forpurification of the lactones. For example, pivalolactone was stirredover calcium oxide for 24 hours and filtered. The polymerization indexbefore treatment was 90 seconds, and after treatment was 65 seconds.Similar treatment with barium oxide reduced the polymerization indexfrom 90 seconds to seconds. Likewise, pivalolactone was stirred over CaHand distilled at reduced pressure. The polymerization index decreasedfrom seconds to 53 seconds. Numerous other alternate procedures werelikewise discarded because of either minimal eifecti-veness or highcost.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. A process for purifying impure a,a-disubstitutedp-propiolactoneshaving the formula R1. R-C=O wherein R and R individually are straightorbranchedchain alkyl of from 1 to 10 carbon atoms, which comprises thesteps of treating said impure u,a-disubstituted- ,S-propiolactone withabout 1 ml. of a 15% solution of an aluminum trialkyl having the formulaAlR wherein R is a straightor branched-chain alkyl of from 1 to 8 carbonatoms, per each 12 to 15 seconds reduction in polymerization index perhundred grams of monomer, and subsequently separating purified:a,-disubstituted-p propiolactone monomer from the resultant mixture.

2. A process of Claim 1 wherein each of R and R is a straightorbranched-chain alkyl of from 1 to 4 carbon atoms. 1

3. A process according to Claim 1 wherein the d,-disubstituted-B-propiolactone is pivalolactone.

4. A process according to Claim 1 wherein the aluminum trialkyl isselected from the group consisting of aluminum trimethyl, aduminumtriethyl, aluminum trin-propyl, aluminum tri-n-butyl, aluminumtriisobutyl, aluminum tri-n-hexyl, aluminum triisohexyl, and aluminumtri-n-octyl.

5. A process according to Claim 1 wherein the aluminum trialkyl isaluminum triethyl.

6. A process according to Claim 1 wherein the separation of the purifiedmonomer is accomplished by vacuum distillation.

7. A process for producing a polymerization grade pivalolactone monomerhaving a polymerization index of less than 15 seconds which comprisesthe steps of adding about 1 ml. of a 15% solution of an aluminumtrialkyl having the formula AlR wherein R is a straightor branched-chainalkyl of from 1 to 8 carbon atoms, per each 12 to T5 seconds ofpolymerization index'time reduction per hundred grams of monomer, to theimpure monomer having a polymerization index greatefithan 15 seconds andsubsequently separating a polymerization grade pivalolactone from theresultant mixture. 1"

8. A process of Claim 7 wherein the separation of the purifiedpivalolactone is accomplished by vacuum distillation.

9. A process of Claim 7 wherein the aluminum trialkyl is selected fromthe group consisting of aluminum trimethyl, aluminum triethyl, aluminumtri-n-propyl, aluminum tri-nbutyl, aluminum triisobutyl, aluminumtrin-hexyl, aluminum triisohexyl, aluminum tri-n-octyl.

10. A process of Claim 1 wherein the aluminum trialkyl is aluminumtriethyl.

References Cited UNITED STATES PATENTS 3,448,122 6/1969 Klootwijk260343.9

DONALD G. DAUS, Primary Examiner A. M. T. TIGHE, Assistant Examiner

